Field of the Invention
The invention relates to a capacitive pressure transducer for measuring the pressure of a medium adjacent to a measuring cell.
Background of the Invention
Pressure transducers are known and are used in many areas of process engineering for process monitoring. In order to measure the pressure of a medium adjacent to the measuring cell, the measuring cell has a resilient measuring diaphragm, which is deflected as a function of the pressure prevailing inside the medium. In this case the deflection or more specifically the reversible deformation of the diaphragm is converted by electromechanical means into a corresponding electrical measurement signal. As the capacitive electromechanical transducer, a measuring electrode, which is arranged on the side of the measuring diaphragm that faces away from the medium, forms together with a counter electrode, which is arranged opposite a base body, a measuring capacitor having a capacitance that changes as a function of the pressure induced deflection of the measuring diaphragm. The measuring diaphragm forms, together with the base body, a measurement chamber that is pressure tight relative to the medium.
These capacitive pressure transducers have the problem that when a medium is used that rapidly changes its temperature, measurement errors occur in the measurement of the pressure because the measuring diaphragm is in direct contact with the medium, and is, therefore, affected by the fluctuations in the temperature of said medium.
It is known that the temperature or more specifically the slow variations in the temperature of the base body are determined by measuring the ambient temperature of said base body, and with these temperature measuring values the pressure measuring value is corrected accordingly. In the event of a large temperature differential between the measuring diaphragm and the base body of the pressure transducer, especially if the temperature of the medium changes rapidly or rather abruptly, this correction method results, nevertheless, in a faulty jump in the calculated pressure measuring value that slowly decreases to the correct measurement value only if the entire pressure transducer is allowed to thoroughly warm up
Furthermore, it is known to measure both the temperature of the base body of the pressure transducer and the temperature of the measuring diaphragm of the pressure transducer, in order to determine a temperature compensated pressure measuring value, and to compensate for the pressure measuring value by means of these two temperature measuring values.
As a result, DE 40 11 901 A1, for example, discloses a capacitive pressure transducer, wherein the measuring diaphragm exhibits a resistance track made of a material having a temperature dependent resistance. In this case this resistance track is placed in the form of a circle around the circular measuring electrode, which forms a capacitor plate of the measuring capacitor, so that the resistance track runs only in the edge region of the measuring diaphragm. However, it has been demonstrated that the arrangement of the resistance track in the edge area cannot correctly measure the temperature of the measuring diaphragm, because the edge region of the measuring diaphragm rapidly cools down due to the dissipation of the heat into the adjacent parts of the housing, a feature that results in a measurement error.
Based on this prior art, the object of the present invention is to provide a pressure transducer of the type described in the introductory part in such a way that it is possible to measure the temperature of the measuring diaphragm of a pressure transducer with higher measuring precision than with the prior art.
This engineering object is achieved by means of a pressure transducer exhibiting the features disclosed herein.